At Bletchley Park, Hinsley studied the external characteristics of intercepted German messages, a process sometimes termed "traffic analysis": from call signs, frequencies, times of interception and so forth, he was able to deduce a great deal of information about the structure of Nazi Germany's Kriegsmarine's communication networks, and even about the structure of the German navy itself.[3]

In late 1943, Hinsley was sent to liaise with the US Navy in Washington, with the result that an agreement was reached in January 1944 to co-operate in exchanging results on Japanese Naval signals[4]

Towards the end of the war, Hinsley, by then a key aide to Bletchley Park chief Edward Travis, was part of a committee which argued for a post-war intelligence agency that would combine both signals intelligence and human intelligence in a single organisation. In the event, the opposite occurred, with GC&CS becoming GCHQ.[5]

On 6 April 1946, Hinsley married Hilary Brett-Smith who had also worked at Bletchley Park, in Hut 8.[1]

He was criticised by Marian Rejewski[8] and Gordon Welchman,[9] who took exception to inaccuracies in Hinsley's accounts of the history of Enigma decryption in the early volumes of his official history, including crucial errors in chronology. Subsequently a revised account of the Polish, French and British contribution was included in volume 3, part 2.

The volumes of British Intelligence in the Second World War edited by Hinsley and published by Her Majesty's Stationery Office (HMSO) London are: